1. Field of the Invention
The present invention relates to a color separation circuit arrangement, and more particularly to a circuit arrangement for separating a color component from an image signal produced by a single plate CCD image sensor.
2. Description of Related Art
There is known a frame storage system and field storage system as color filter arrangement system of a color difference sequential system for a single plate CCD image sensor. An arrangement according to the field storage system as shown in FIG. 1 is well known and used more frequently than an arrangement according to the frame storage system in order to overcome the "after-image" problem of the frame storage system.
FIG. 1 (PRIOR ART) is a plan view showing a conventional arrangement in the prior art of color filters of CCD image sensors. In FIG. 1 (PRIOR ART), for example, color filters Ye (yellow), Cy (cyan), Ye, Cy, ... may be sequentially arrayed from the left end for the pixels on the 4n-th (n is a natural integer) horizontal line; further, for example, color filters Mg (magenta), G (green), Mg, G, ... may be sequentially arrayed from the left end for the pixels on the (4n+1)-th horizontal line. Additionally, for example, color filters Cy, Ye, Cy, Ye, . . . may be sequentially arrayed from the left end for the pixels on the (4n+2)-th horizontal line, and color filters Mg, G, Mg, G ... may be sequentially arrayed from the left end for the pixels on the (4n+3) th horizontal line.
For odd-numbered fields, photoelectric conversion signals (Ye+Mg or Cy+G) are extracted simultaneously from the 4n-th and the (4n+1)-th horizontal lines, and sequentially for the conversion signals, as signals pertaining to one horizontal scanning line; photoelectric conversion signals (CyMg or Ye+G) are then extracted simultaneously from the (4n+2)-th and the (4n+3)-th horizontal lines, and sequentially for the conversion signals, as signals pertaining to one horizontal scanning line, after which this extracting operation is repeated. On the other hand, for even-numbered fields, photoelectric conversion signals (Mg+Cy or G+Ye) are extracted simultaneously from the (4n+1)-th and the (4n+2)-th horizontal lines, and sequentially for the conversion signals, as signals pertaining to one horizontal scanning line; photoelectric conversion signals (Mg+Ye or G+Cy) are then extracted simultaneously from the (4n+3)-th and the (4n+4)-th horizontal lines, and sequentially for the conversion signals, after which this extracting operation is repeated.
According to such a filter arrangement, for odd-numbered fields, vertically adjacent two pairs of color filter regions of Ye and Mg, Cy and G, Cy and Mg, and Ye and G serve as extracting unit regions. For even-numbered fields, two pairs of color field regions Mg and Ye, G and Cy, Mg and Cy, and G and Ye serve as extracting unit regions.
The pairs of photoelectric conversion signals on the same vertical line and two horizontal lines thus extracted are summed to compose summed photoelectric conversion signals . . . X.sub.p-1, X.sub.p+1, X.sub.p+1, . . . which are applied to a color separation circuit. In this specification, the term "color separation apparatus" means an apparatus including an image sensor, and the term "color separation circuit" means a circuit excluding the image sensor. The color separation circuit separates red signal R or blue signal B alternately for every horizontal scanning line by appropriately executing prescribed color separation operations from summed photoelectric conversion signals of two vertical lines adjacent in horizontal direction, that is, summed photoelectric conversion signals, . . . , X.sub.p-1 and X.sub.p, X.sub.p and X.sub.p+1, . . . having different color components from each other.
However, according to the conventional color separation apparatus, the separation operation is carried out based on the summed photoelectric conversion signals, . . . , X.sub.p-1 and X.sub.p, X.sub.p and X.sub.p+1, . . . , for portions of two vertical lines adjacent in horizontal direction; as a result, a pseudo color is generated when an image contour falls on the boundary between the two adjacent vertical lines. Thus, the color component in the image signal cannot appropriately be separated due to the pseudo color.
For example, in the case where a color separating operation is carried out with respect to summed photoelectric conversion signals X.sub.p-1 (Cy+G) and X.sub.p (Ye+Mg) on four pixels P.sub.xl -P.sub.x4 as shown in FIG. 2, if the black-and-white contour RL of the image which is extending in the vertical direction passes on the center of these pixels, then the summed photoelectric conversion signal X.sub.p-1 corresponds to white side of the contour while the other summed photoelectric conversion signal X.sub.p corresponds to black side, without employing a common color as the filtering target. As a result, a pseudo color is produced because the color separating operation cannot properly be carried out.
The pseudo color problem may also occur when the colors on the left-and-right side of a contour are different from black and white.